Oil-rich North Africa is plagued by al-Qaida groups from Morocco to Egypt, all heavily armed with weapons seized in Libya's 2011 civil war.
In 2012, al-Qaida in the Islamic Maghreb, the region's key jihadist organization, and its Tuareg allies did in northern Mali what no jihadist group had ever done: seized terrain and held it.
They were driven out in a French-led military intervention in January-February this year, but their brief rule was a chilling warning of growing jihadist ambitions, strengthened by new planning and military capabilities.
They've now taken over southern Libya, still gripped by anarchy two years after Moammar Gadhafi was overthrown and killed.
It was from there that a 32-strong unit from an AQIM splinter group led by veteran Algerian jihadist Mokhtar Belmokhtar stormed the In Amenas gas complex in southern Algeria, operated by BP and Norway's Statoil, in January. Most of the attackers and about 40 foreign technicians were killed in a withering assault by Algerian forces.
Two weeks later, Belmokhtar's cadres carried out coordinated suicide attacks against a French uranium complex in nearby Niger and a military base.
In Egypt's Sinai Peninsula, al-Qaida-linked groups, swelled by foreign recruits and disgruntled Bedouin, are now waging a growing insurgency against the Egyptian army that could eventually drag in neighboring Israel as well.
In West Africa, an increasingly important oil-producing region, militants of Nigeria's Boko Haram movement, trained by Algerian and Somalia jihadists, killed about 180 people last week in one of their deadliest raids in a six-year-long insurgency in the northeast of the continent's most populous country .
The seizure of the landmark Westlake shopping mall in Nairobi Saturday by an estimated 15 heavily armed jihadists, marked a major departure for al-Shabaab in widening their 7-year-old war in Somalia, which has been mired in chaos since the 1991 overthrow of military dictator Mohamed Siad Barre by warlords.
The Nairobi rampage, during which the attackers sought out and slaughtered dozens of non-Muslims, including foreigners, among the hundreds of people in the mall, bore eerie similarities to the three-day commando-style assault by Pakistani jihadists on Mumbai, India's financial capital, in November 2008 when more than 160 people were systematically massacred.
"Islamists in Kenya have been planning to shift from soft targets to a big-ticket attack for the past two, three years," said a Western diplomat in Nairobi who has monitored al-Shabaab and recent spate of relatively minor grenade attacks in Kenya over the last 18 months.
"The attack on Westgate represents the aspiration for a 'Big Bang.'"
Kenya, the biggest economy in East Africa and a U.S. ally, became a battleground because it contributed thousands of troops, with armor, artillery and warplanes to an African Union force that aided neighboring Somalia's Western-backed transitional government in October 2011 and drove al-Shabaab out of Mogadishu, the capital, and other urban centers.
Uganda, where 76 people were killed in July 2010 bombings, Burundi and Ethiopia also contributed troops, so they're vulnerable as well.
Nairobi's attempting to set up a border buffer zone inside Somalia in a region known as Jubaland, a plan that will likely trigger further al-Shabaab attacks.
The zone's intended to curb infiltration. But al-Shabaab has support groups, safe houses and arms caches inside Kenya among the 250,000 Somalis living around Nairobi and the coastal city of Mombasa.
There's also growing radicalization among Kenya's 4.3 Muslims. Several extremist groups have emerged, most notably al-Hijra. It recruits for al-Shabaab, leaving Nairobi vulnerable to further attacks.
A U.N. report in July noted al-Hijra is strengthening ties with similar groups in Tanzania, Rwanda and Burundi "as an operational priority."
In November 2002, Mombasa was hit by jihadist attacks organized by al-Qaida's East Africa chief, Fazul Abdul Mohammed, who masterminded the Aug. 7, 1998, bombings of the U.S. embassies in Nairobi and Dar es Salaam, Tanzania, that killed 224 people.
Fazul, one of Osama bin Laden's most capable operatives, played a key role in organizing al-Shabaab.
He was killed in Mogadishu in 2011. But the planning of the Westgate attack bears the imprint of his deadly skills.